Luminous
by TheScreamingViking
Summary: Mermaid AU.


Shepard swam alongside the ship's hull. The humans had taken to mounting flood lights on their vessels lately, whether to make merfolk easier to spot or to try and scare them away, she couldn't say.

It wasn't working either way. She looked up at the oblivious sailors from the pool of light. The harsh light outlined three harpoon guns mounted on this side of the ship alone. They were all manned too, even though it was nearly dawn. It was the largest Shinra vessel she'd seen on this route in years and it was moving slowly, riding low in the water. One of her scouts had reported it to her, but it was a slow night, and so she tailed it herself. Shinra had long since lost the luxury of sailing unattended through their waters.

Typically they either stuck to the major shipping lanes or just used their strange flying machines. If they came here at all, they tried to race through as fast as possible.

She dove under the waves, studying the ship from below. Even the shape was unusual. It didn't cut through the water; it slogged along with a heavy square base like a barge.

She surfaced on the other side. The humans were talking quietly among themselves and squinting nervously out into the water.

"Hey, is that a—is that a dolphin? Up by the bow?" one of them asked.

She smiled to herself.

"I think it's a shark."

"Right, yeah. Just a shark."

She rolled over in the wave, letting her long grey tail splash above the surface. She winked at the man.

"Mermaid!"

She ducked back under the bulk of the ship and waited.

No harpoons.

She cocked her head and spun in place, keeping pace with the slow ship. Why all the extra guards? And why weren't they firing? Shinra grunts were as aggressive as betta fish; she had known them to harpoon regular fish sometimes just in case.

Humming a curious tune she breached again on the other side, letting her tail arc in the air behind her.

"There it is!"

She ducked under again, and heard feet thundering across the deck. Still, no harpoons followed.

Her scales itched—it was some kind of trap, surely?

The hull shook. She swam on her back, studying it. It wasn't the usual smooth metal. Instead it was slotted with a seam down the middle. It couldn't possibly be watertight.

The hull lurched. The metal sheets slid apart, and a cage fell into the water. She recoiled. The water frothed with sudden activity, and her body jolted. Her lungs seized up. Shocks shot down her spine all the way to her tail making her jerk and buck. Blinding flashes of light obscured her vision.

Someone was screaming.

She whipped her tail forward in a sharp crack then bolted away, swimming blind and limp.

Breath returned to her and she panted, slowing in the water. Nothing was chasing her. The flashes and tremors subsided and she flipped around to look back at the ship. The cage still hung below the hull in a riot of bubbles. There was a creature inside, writhing like mad. She could just make out green streamers reaching out through the bars.

They were screaming. She stopped swimming.

It was a merman.

With a loud grinding noise the cage lurched back up into the hull of the ship, and the metal grates slid closed again.

The humans had a merman in a cage.

She bared her teeth and shot up to the surface again. The ship had overtaken her while she regained her breath, she followed it now, her dorsal fin cutting through the water.

The humans were cheering. Clapping each other on the back, slapping their hands together and laughing desperate, relieved laughter.

Shinra had a merman in a cage, and they thought they'd won.

She sank back into the waves and swam towards her nearest outpost.

* * *

Darkness reigned by the time she made it back to the ship, Jack in tow.

It hadn't been hard to persuade her to come along; Jack was always ready to sink ships, especially where Shinra was involved. Shepard didn't usually encourage that kind of behaviour, not on her stretch of the surface.

She looked to the disfigured betta fish mermaid, who was stretching her arms out behind her as she swam. Scars raced down her orange and black fins like lightning, branching and ragged.

They made quite a pair, Shepard thought, tracing the diagonal bite mark across her grey scaled abdomen. A massive deep sea mermaid had given that to her, back when she was little more than a child. It had been wailing and injured, shooting up to the surface from the darkness of the trench. It only bit her in confusion, really, but it was a miracle she'd survived at all.

She slowed as they approached the ship.

"How do you wanna do this?" Jack asked, her fins flicking back and forth in excitement.

She looked up at the surface. "We're going to board."

A vicious smile cut across Jack's face. "Haven't done that in a while. Feeling mean, Shepard?"

"A little," she conceded. "Once we're on board, I'll find the prisoner and you keep the guards away. I think he's hurt."

Jack nodded and waited for her signal, humming a note of anticipation.

Sticking close to the side of the ship, they shot up out of the water together, each grabbing a guard and dragging him back down into the water. The cry went up. They sped to the other side of the ship and hauled themselves up onto the deck.

Snarling, Jack threw two more into the water. She tore a harpoon gun off the deck and swung it around like a club. Two more guards went down. Another threw himself into the water.

Shepard dragged herself over the deck. She whipped her long tail around at a man drawing a gun on her. The gun went flying and the man fell back in a spurt of blood.

She opened a door and followed the narrow corridors, dragging herself quietly down the stairs. Given where the cage was located on the hull, she was looking for a room on the bottom level near the centre of the ship.

The corridor led her to a room with a padlocked door. She tore off the padlock.

A large tank dominated a brightly lit room.

She didn't much care for the light, but the merman in the tank looked near paralysed by it. He sat at the bottom with his eyes screwed shut and a grimace across his face. He jerked at her entrance.

She approached, humming a soft questioning note.

He jerked up in his tank, smacking into the bars on the inside of the glass and whipping his head around. He made a guttural mumble in alarm, nothing like the soft harmonics of their language.

She halted her approach and looked back at the lights set up around him on stands. She whipped her tail around and darkness blanketed them.

She blinked through the silhouettes the bright light had left on her retinas.

He glowed. Green and silver streamed violently down his long body, his arching tail, spiny streamers, and thick silver hair. Unmistakeably a deep sea merman.

His eyes were still closed.

She approached again, sighing a soft tune of comfort, reassurance. He might not understand the particulars, but surely the feeling of it was clear?

Cautiously, he opened his eyes. They were huge, bright green with a slit pupil. Eyes made for the dark.

He stared at her, rising up in his tank. He was big, and yet, he wasn't big enough. His kind usually rivalled blue whales. He looked to be roughly four meters long, in a tank five meters long. He must have spent his entire life locked up.

A suspicion formed in her mind. She remembered the old deep sea mermaid, raging and injured, shooting for the surface. They never did that. They never left their trenches.

The stripes of light shooting down his hair and flank slowed. Those big eyes studied her intently. He stuttered out a curious note, not quite right.

"You shouldn't be here," he said. His voice was deep and husky from disuse.

"Neither should you," she replied. Cold anger sat heavily in the pit of her stomach. She was going to tear this ship to pieces with her bare hands.

First though, he needed to get out of the tank. She crawled around her, examining its walls. No handy seams to tear open. She crawled on top of it, hauling herself up. There was a latch, but no padlock. She understood those, tear them off and the doors opened. This had one of the infuriating new locks with the tiny buttons and little red lights. It was perfectly smooth, she couldn't get her fingers into anything to rip open. She snarled in frustration.

The merman inside watched her curiously.

"I'm going to get you out," she said. She raised her fist and threw all her strength into the punch.

Nothing. She punched it again. The glass didn't even tremble.

She dragged herself back onto the ground and studied the tank with pursed lips.

A shadow darkened the open doorway. Shepard spun around, but Jack took the human down from behind.

The merman watched passively.

"You should leave," he said. "They'll catch you."

"Do we look like we're scared of being caught?" Jack asked, rehinging her jaw. She took off again. The now headless man had been dressed different from the others, in a long white coat.

The merman watched the corpse, his expression mostly confused.

"Don't you want to escape?" Shepard asked.

He looked back to her, his large eyes unblinking. The flashes of green light down his side picked up speed again. He nodded cautiously.

She studied the tank. There had to be _something_. She pried at the corners, scrabbling for a handhold.

"Shepard, time to haul ass!" Jack called.

She swore. She backed away from the tank, feeling like a traitor.

"I'm going to get you out. I will."

He shook his head. Those giant eyes blinked. "Thank you. For the dark."

"I'll get you more than that. I promise," she said, putting a hand on the glass.

He tilted his head and placed his hand on the other side.

"Shepard!"

She fled the room to the sound of guns going off, and she and Jack threw themselves overboard.

* * *

Sephiroth knew they were following the ship. The merfolk who had destroyed the lights and killed Hojo.

The bottom of his tank was a thick grate letting in the ocean water. He had suspected as much, could sometimes hear strange sounds coming up through it. Then the grate had pulled away and the entire cage was dumped into the wide open sea without warning. It had terrified him, the sudden drop, the lack of walls, the change in pressure and light.

He pressed his ear to the bottom of the cage and could hear them. Out in the open ocean, the two mermaids. Singing to each other? He didn't really understand it, but something about the notes sounded harsh. The grey one, Shepard, had hummed softly to him in the tank room, quiet notes that felt calm and said she wasn't an enemy. The notes she sang now said she was certainly someone's enemy. It felt… fierce. Sharp and angry.

He tried to sing to them. He didn't know if he was built to, had never tried before, and the warbling sensation in his throat felt strange.

Their song stopped.

He tried again, a note of… greeting? He wanted to say hello. Or just, announce his presence.

An awful tearing noise rang out and he sprang back to the top of his tank.

The thick grating ripped away. Shepard's face appeared, red eyes gazing at him from behind flowing grey hair, on the other side of the bars of the cage.

"Hello," she said, before she gripped the bars and yanked.

They didn't move. She bared her teeth and pulled again, but to no result. The second mermaid, orange and black with scarred fins, joined her, both of them straining.

The bar didn't even bend.

"Damn, I thought we had it," Shepard said, finally relenting.

He watched from the top of the cage.

"Has the ship stopped moving?" he asked.

"We pulled down the anchors and tied them to wrecks on the bottom," the orange mermaid said, giving him an alarming smile.

"They tried to turn around and head back for land after the attack last night," Shepard added. "This is Jack, by the way, and I'm Shepard. What's your name?"

Nobody had ever asked him before. Hojo had displayed him to the president and various company directors, and the lab techs liked to bring in their friends to gawk at him when they thought they could get away with it. The other merfolk trapped in the labs had usually been kept sedated until they died. He'd never actually met anyone.

"My name is Sephiroth," he said. He'd never seen merfolk outside of tanks either.

He was still floating at the top of his cage, his back pressed against the bars.

The two mermaids watched him from the unfettered confines of the ocean. Beams of sunlight shone through the water, and a school of little fish danced away from them. There were no walls. It just kept on going. It was the biggest thing he'd ever seen.

Shepard, who had been floating further back, flipped backwards to come up closer to the cage, her long thin tail trailing behind her.

He didn't know what to say.

"How can we help, Sephiroth?" she asked.

He shook his head. "I don't know."

She frowned in thought. "Let's give it a couple of days. They're trapped now; let them think it over."

She and Jack shared a hum, before Jack swam off.

"Have they hurt you? Since we broke in?" Shepard asked him.

"They locked the door again. Nobody has come in." He hadn't seen any of Shinra's people since they hauled out Hojo's body. The lights remained mercifully broken in smashed heaps on the floor. He knew the guards were scared of him. They always had been, but after the attack those who remained were terrified. They weren't even feeding him.

He hadn't fully understood why he scared them so much. He never hurt anyone; he'd spent his whole life in a tank. He looked at the free mermaid and understood.

She was difficult to make out, her grey scales disappearing in the water.

"What are you?" he asked.

She smiled slightly. "I'm a thresher shark mermaid. We don't normally live in these waters. We're more topical."

He swallowed. "And… what am I?"

Her smiled faded away. "You, my friend, are a deep sea merman, native to the trenches." Her expression turned fierce, sharp teeth visible at the corners of her mouth. "You don't belong in a cage."

He looked at the ocean behind her, disappearing away into untold waters. Deep, deep down, unmeasured depths where the creatures of the dark lived. Where it must be so cold, so quiet, so dark. He could feel his streamers starting to glow.

"I know," he whispered.

* * *

She kept him company. It was the least she could do until she could break him out properly.

The humans onboard weren't feeding him anymore, too scared to even enter his room, so she caught fish and fed them through the bars. She watched his simple curiosity at eating fresh fish with a smile.

She could hear the humans panicking aboard the ship, desperately trying to restart the motors. She'd stuffed rocks into them. Her first row of teeth bit into her smile. She fancied this was how true sharks felt when they smelled blood in the water.

He didn't know how to sing, so she taught him. The beginnings of it at least, how to hum together with her the fine threads of a conversation that didn't need words. A fisherman had once told her that humans believed mermaids could enchant minds with their voices. She listened to his rumbling baritone and could well imagine where such flights of fancy came from.

He told her how the tank worked.

"The lock is electronic," he said.

"I don't really know what that means," she replied. Everything humans made these days seemed to be 'electronic' but none of it ever worked by the time she got her hands on it.

"It means it can be turned off," he said, looking thoughtful.

She swam closer to the bars. "How?"

"There must be a generator. It'll be a big box that roars and powers the whole ship."

"How do I break it?"

He smiled at her, looking at her arms. "I'm sure you'll discover a way."

She smiled back.

Jack returned the next day, and Shepard hauled herself back up onto the deck. She didn't bother with a diversion or waiting until cover of night, she sat on the railing of the stranded ship in broad daylight.

Half of the remaining humans laid down their weapons without a fight. The other half she threw into the water. Jack was waiting for them.

In the end, Shepard didn't even need to get creative to turn off the generator. None of the humans knew the passcode to the lock, but they could turn off the generator without any complications.

Some part of her wanted to just sink the ship. They'd put Sephiroth in a tank and then left him in it to starve. But she wasn't Shinra. She would never be Shinra. She let the survivors go.

She tore the top off of Sephiroth's tank and held out a hand for him.

He looked up at her, glancing between her face and her hand.

"I've never been outside of a tank before," he said quietly.

She smiled. "Come on. The water's fine."

He took her hand.

* * *

It was so big. That was his first thought when he landed in the ocean. It was so bright and it was everywhere. He reached out for the walls and they weren't there. They weren't anywhere. The water just kept on going, as far as he could see in every direction.

His breathing picked up speed, and his streamers twitched around him, glowing in bright frantic flashes. He closed his eyes tight.

Shepard sang to him.

 _Safe. You are safe._

He gave a strangled reply, spinning around. There was no glass wall to bump into, to press himself against.

Shepard swam next to him and put her arms around him. He latched onto her, needing something, anything solid. She was strong and definite, a frame to hold onto in the emptiness.

 _I have you,_ she sang in a wordless tune.

He tried to sing back. It came out thin and alarmed. She matched his tone, and crooned against him. He could feel the vibrations of it against his scales.

She went down an octave, and he followed her. She held him and led him down into deeper soothing melodies, simple tunes, comforting and calm.

 _You are safe._

He opened his eyes. She was still holding him, wrapped up in his arms and streamers. She nudged his nose with hers and hummed a question.

He smiled at her and nodded.

She disentangled herself and swam ahead, tugging on his hand. He followed her down away from the surface.

He focused on her, not the endless waters stretching away around them. Just her.

They left the light and warmth of the surface behind. The ocean floor came into view, sloping away at a steep angle, and she kept swimming down. The sloping floor became the cliff of a trench, and still they swam downwards.

By the time they stopped, it was completely dark. Dark like he'd never known it could be, and he could see properly for the first time. He looked at Shepard and could see her with clarity. Her long grey tail, her sharp fins, her lean and muscled body. A large bite mark wound around her side and harpoon scars adorned her dorsal fin. Grey hair streamed behind her, matching the shade of her scales. Sharp red eyes. She was so beautiful.

"Welcome home," she said.

He looked around. They weren't at the bottom of the trench yet, the cliff kept on going straight down. He swam near it now, taking comfort in the wall. Who knew how far down it went?

It was so big.

He stretched, really stretched. He had the room. There would be no more examinations. No more scale and cartilage samples. No more processed food pellets. Hojo could never pin him down and cut him open again.

He was… free.

He swam in the largest circle he could for the sheer joy of it. The water rushed past him, freezing cold currents. He spun in place, let his streamers flare out as far as they reached. He swam out into the open waters away from the cliff, then he came back because that was still a little too much freedom. He reached out and touched the face of the cliff. It crumbled beneath his hands, gritty and soft at the same time, the dirt getting caught under his finger nails.

He wanted to laugh, he wanted to scream. He wanted to sing.

So he did. Shepard sat on a little ledge in the cliff wall, letting him explore to his heart's content without comment.

When he recovered from the sheer novelty of it, he joined her, curling around her and the ledge. It was so dark, he took pleasure in blinking and not feeling any pain when his eyes opened again.

"Will you go back?" he asked, glancing up towards the surface.

"In a couple of days, yes. I'll stay until you're comfortable here," she replied.

He leaned his chin on his knuckles, watching her. "Do you have to go back?"

She gave him a grim smile. "Are there others in cages and tanks?"

His joy wilted. There were others. Not like him, not big and glowing and suffocating in the light, but there were countless lithe and green merfolk cut open and disposed of in Shinra's labs. "Yes. There are."

"Then I have to go back." She looked out across the trench, the murky currents slowly drifting by. "I'm one of the leaders of the surface guard. Until Shinra's last ship gets hauled out of the water or hits the sea bed, my place is up there."

She got up from the ledge and did a little flip until she was facing him. "Come on. I want to show you something, if you don't mind going back up to the edge of the trench?"

"Lead the way," he said. He would make the most of the time he had with her.

The warmer, lighter parts of the sea weren't so unsettling on the way back up. They followed the cliff up and along. They passed other merfolk who recognised and greeted Shepard warmly.

They glanced at him curiously and introduced themselves. He had met more people than he'd ever seen in his life by the time they arrived at their destination.

She stopped before a coral reef. It rose up from the flat of the shelf unexpectedly, a series of lumps and mounds, that disappeared as suddenly as they sprung up.

They hung back from it, watching the little fish flittering about it. There were no merfolk here.

"What is it?" he asked.

"It was a deep sea mermaid once," Shepard said plainly. She gestured at her abdomen, where the diagonal bite mark cut into the transition from scales to skin. "She gave me this."

Sephiroth looked back up at it. He could almost see the shape of it, under the brightly coloured coral and schools of fish.

"I was barely more than a fingerling when she came screaming up out of the trench, streaming blood. She was crying."

He felt a tingle run down his scales. "Crying?" he asked, cautiously.

Shepard gave him a sad look. "For the child that Shinra had stolen from her."

He grew still.

"This was back when we let their submarines into our waters. Before we knew how badly they had betrayed our trust," she said quietly. "We started the war for her."

"What was her name?" he asked. His voice sounded hoarse and faint to his ears.

"Nobody knew her name, but we call her Omega. The humans probably call her something else."

He hauled water into his lungs, forcing himself to keep breathing. He'd never known where he came from. Hojo had mentioned a mother, and he'd dreamed of meeting her when he was younger, but he had never known if any of it was true, if she was still out there, if she had existed at all.

He looked at the coral reef, built high on a corpse.

He had known. Deep inside of him, he had always known this.

"Jenova," he said. "They call her Jenova."

* * *

Sephiroth followed Shepard back into the trench, the image of his mother's final resting place in his mind.

He felt grieved, but ultimately, glad. He finally had confirmation—he'd grasped the full picture and understood his place in it. It was… satisfying, to get that closure.

Shepard kept her word and stayed with him. She taught him how to live beneath the waves, how to survive without a team of scientists heavily invested in his fate. She showed him how to ride the currents and sense his direction, how to sing in octaves neither humans nor fish could hear.

Some of it he didn't need to be told. He needed no help finding food, his natural bioluminescence attracted fish without his even trying. He watched the way she hunted, approaching the schools while practically invisible in the dark, then stunning them with her tail, quick as a whip. The crack of it could shock a dozen at a time.

She helped him find a place to sleep, deep down in the pitch black walls of the trench. He curled around her that night, keeping her tucked into the glow of his side. He wanted to keep her there, safe in his dark ravine, but he saw the way she looked over her shoulder. She was unsteady in the depths in a way she hadn't been even on the decks of a Shinra ship.

She wasn't safe here.

Finally, she left for the surface.

Alone in the dark, he learned how to be at home. He grew accustomed to the lack of walls, the lack of external limitations. He could hypnotise fish with his fluctuating glow, and his long streamers worked like extra hands.

He broke open old submarines with his hands and ate the fish hiding inside. He fought the other creatures of the deep. He learned, and he grew.

He discovered just how dangerous he truly was.

Throughout it all, he looked up to where he knew the light was, and his clever thresher shark.

When he was ready, he swam back up again.

He still didn't like the light, he never would, but he had learned how to swim and fight blind. His hearing was excellent and he could sense movement in the water. He asked the merfolk he passed, and kept swimming up to the surface.

Finally, he heard it. Her singing, sharp and fierce, followed by metal tearing. He chased it.

He found a Shinra vessel harassing a little fishing boat. Shepard was leading the Shinra vessel away, leading them on a merry chase into dangerous waters.

She sprang forward and attacked their outboard motor. Harpoons fired into the water. From below, he heard her climb on board. The splashes of men being thrown into the water, thrashing about, and starting to drown.

He swam up and joined the fight. He broke the metal hull apart with his hands. The vessel began to sink, and Shepard leapt back into the water, smiling fiercely.

He sang out a greeting. She sang back, delighted to see him. He rose up to her, and they swam together, tails curling around each other.

* * *

 _A/N: Thanks for reading, this is part three of a Sephiroth/Shepard prompt challenge. I am still looking for more prompts, let me know if you have any ideas!_


End file.
